Puma Worker Killer
If you have a memory leak in your code, finding and plugging it can be a herculean effort. Instead what if you just killed your processes when they got to be too large? The Puma Worker Killer does just that. Similar to Unicorn Worker Killer but for the Puma web server.
Puma worker killer can only function if you have enabled cluster mode or hybrid mode (threads + worker cluster). If you are only using threads (and not workers) then puma worker killer cannot help keep your memory in control.
BTW restarting your processes to control memory is like putting a bandaid on a gunshot wound, try figuring out the reason you're seeing so much memory bloat derailed benchmarks can help.
In your Gemfile add:
$ bundle install
Turn on Rolling Restarts
A rolling restart will kill each of your workers on a rolling basis. You set the frequency which it conducts the restart. This is a simple way to keep memory down as Ruby web programs generally increase memory usage over time. If you're using Heroku it is difficult to measure RAM from inside of a container accurately, so it is recommended to use this feature or use a log-drain-based worker killer. You can enable roling restarts by running:
before_fork do require 'puma_worker_killer' PumaWorkerKiller.enable_rolling_restart # Default is every 6 hours end
or you can pass in the restart frequency:
PumaWorkerKiller.enable_rolling_restart(12 * 3600) # 12 hours in seconds
Make sure if you do this to not accidentally call
PumaWorkerKiller.start as well.
Enable Worker Killing
If you're not running on a containerized platform you can try to detect the amount of memory you're using and only kill Puma workers when you're over that limit. It may allow you to go for longer periods of time without killing a worker however it is more error prone than rolling restarts. To enable measurement based worker killing put this in your
# config/puma.rb before_fork do require 'puma_worker_killer' PumaWorkerKiller.start end
That's it. Now on a regular basis the size of all Puma and all of it's forked processes will be evaluated and if they're over the RAM threshold will be killed. Don't worry Puma will notice a process is missing a spawn a fresh copy with a much smaller RAM footprint ASAP.
When you boot your program locally you should see debug output:
 Puma starting in cluster mode...  * Version 3.1.0 (ruby 2.3.1-p112), codename: El Niño Winter Wonderland  * Min threads: 0, max threads: 16  * Environment: development  * Process workers: 2  * Phased restart available  * Listening on tcp://0.0.0.0:9292  Use Ctrl-C to stop  PumaWorkerKiller: Consuming 54.34765625 mb with master and 2 workers.
If you don't see any
PumaWorkerKiller output, make sure that you are running with multiple workers. PWK only functions if you have workers enabled, you should see something like this when Puma boots:
 * Process workers: 2
If you've configured PWK's frequency try reducing it to a very low value
start you can configure
PumaWorkerKiller. You can do so using a configure block or calling methods directly:
PumaWorkerKiller.config do |config| config.ram = 1024 # mb config.frequency = 5 # seconds config.percent_usage = 0.98 config.rolling_restart_frequency = 12 * 3600 # 12 hours in seconds config.reaper_status_logs = true # setting this to false will not log lines like: # PumaWorkerKiller: Consuming 54.34765625 mb with master and 2 workers. end PumaWorkerKiller.start
If you start puma as a daemon, to add puma worker killer config into puma config file, rather than into initializers:
Sample like this: (in
before_fork do PumaWorkerKiller.config do |config| config.ram = 1024 # mb config.frequency = 5 # seconds config.percent_usage = 0.98 config.rolling_restart_frequency = 12 * 3600 # 12 hours in seconds end PumaWorkerKiller.start end
It is important that you tell your code how much RAM is available on your system. The default is 512 mb (the same size as a Heroku 1x dyno). You can change this value like this:
PumaWorkerKiller.ram = 1024 # mb
By default it is assumed that you do not want to hit 100% utilization, that is if your code is actually using 512 mb out of 512 mb it would be bad (this is dangerously close to swapping memory and slowing down your programs). So by default processes will be killed when they are at 99 % utilization of the value specified in
PumaWorkerKiller.ram. You can change that value to 98 % like this:
PumaWorkerKiller.percent_usage = 0.98
You may want to tune the worker killer to run more or less often. You can adjust frequency:
PumaWorkerKiller.frequency = 20 # seconds
You may want to periodically restart all of your workers rather than simply killing your largest. To do that set:
PumaWorkerKiller.rolling_restart_frequency = 12 * 3600 # 12 hours in seconds
By default PumaWorkerKiller will perform a rolling restart of all your worker processes every 12 hours. To disable, set to
You may want to hide the following log lines:
PumaWorkerKiller: Consuming 54.34765625 mb with master and 2 workers.. To do that set:
PumaWorkerKiller.reaper_status_logs = false
Note: It is
true by default.
Open up an issue or ping me on twitter @schneems.